The present invention relates to an electronic circuit for producing square wave signals. In particular, the present invention is a sine-to-square wave converter circuit which derives a square wave pulse waveform from a sinusoidal alternating current (AC) waveform.
In many electrical systems, there is a need for clock pulses to provide timing and synchronization of the system. In many systems, such as traffic controllers, these clock pulses may be derived from a 60 cycle AC waveform. The input waveform must be converted from a sinusoidal waveform to a square edge pulse waveform in order to operate the logic circuits of the controller.
One commonly used technique for converting from sine to square waves is to apply the AC sinusoidal waveform to a CMOS inverter. This technique, however, has some shortcomings. First, the CMOS inverter has relatively low hysteresis and, therefore, relatively low noise immunity. Second, momentary spikes of several hundred volts on the AC waveform can destroy a CMOS inverter. An elaborate input protection network is often required to protect the CMOS device from these voltage spikes.